New nationwide radio communication networks, such as paging networks, are being designed which benefit from high power (greater than 1 kilowatt) transmitters having linear power amplifiers operating at carrier frequencies of approximately 1 Gigahertz. The high power output achieved in these high power amplifiers can be accomplished by using a multistage power amplifier having parallel output stages, but for maximum efficiency, the parallel stages must be phase and gain matched.
Known means of matching parallel output stages in such multistage radio frequency power amplifiers include gain and phase adjustment of the stages after final assembly of the power amplifier in the factory and after repair of one or more stages of the multistage power amplifier in the field. The gain and phase adjustment optimizes overall gain and efficiency of the power amplifier, allowing the power amplifier to meet full power output specifications without overheating. This technique can be performed manually, requiring considerable time and therefore expense. An alternative technique is to design the output stages to predetermined, precise gain and phase delay requirements. This technique, while quite successful, requires the use of precision active and passive electrical components in the parallel stages, as well as precision setting of each stage after each stage is built, during individual stage testing, which is expensive. Cables used to interconnect the stages in parallel in this alternate technique are fabricated to meet precision phase change requirements and are therefore also expensive.
Thus, what is needed is an inexpensive technique of optimizing the gain and phase matching of a multistage power amplifier.